1. Field of the Invention
The present invention relates to an apparatus for cooling the work rolls of a roll stand, wherein the apparatus includes for each roll a cooling water duct equipped with spray nozzles at a spray beam as well as means for supplying cooling water and for removing heated water, a cooling water guide plate for the upper work roll arranged at an acute angle relative to the rolling stock surface and provided with a stripping member at the front of the guide plate facing the upper roll, and an essentially horizontally extending cooling water guide plate located closely underneath the rolling stock plane and provided with a stripping member for the lower roll.
The present invention also relates to a method for cooling the work rolls using the apparatus described above.
2. Description of the Related Art
Apparatus and methods for cooling the work rolls of roll stands are known in the art. Usually, a cooling unit each is provided on the entry side and on the exit side. Even though requiring a large and complicated apparatus, the effect of the work roll cooling unit on the entry side is relatively small.
The requirement of an effective work roll cooling results from the objects to be achieved in connection with the rolling process; these objects are:
preventing a defined temperature limit from being exceeded in order to maintain the mechanical properties of the work rolls;
limiting the thermal stresses in the work rolls and, thus, preventing fractures in the work rolls;
minimizing fire cracks in the surface of the work rolls;
positively influencing the oxidation film on the work rolls, particularly in chromium steel rolls.
Most of the heat is produced during the contact of the work rolls with the rolling stock in the roll gap; this is increased by the additionally developed rolling heat produced as a result of the plastic changes of the shape of the rolling stock and further by the frictional heat produced between the rolling stock and the rolls and the introduction of the frictional heat in the contact area between the work roll and the back-up roll and additional heating by the radiation heat in the entry area and in the exit area.
For achieving sufficient roll cooling, the influence of the cooling unit on the exit side is of particular importance because the heat induced to the surface area of a roll must be removed as early as possible after leaving the roll gap in order to prevent the heat from penetrating into the depth of the roll as much as possible and as efficiently as possible.
DE 36 16 070 A1 discloses a roll cooling apparatus for a roll stand which includes cooling water guide plates which each have a curved surface along the circumferential direction of a roll and are arranged near the respective roll, further a cooling water supply distributor for supplying the cooling water in a cooling water duct which is defined by the cooling water guide plate and the roll, a water discharge distributor for discharging the cooling water from the cooling duct and supplied by the cooling water supply distributor, a support element for supporting the cooling water guide plate and curvature adjusting members which change the curvature of the guide plate in accordance with the diameter of the roll. The thickness of the guide plate increases from the edge portions to the middle of the guide plate in the circumferential direction of the roll. When the roll diameter is changed the curvature adjusting members serve to maintain the space available between the guide plate and the roll to the necessary extent so that the roll is sufficiently cooled. This apparatus produces a forced cooling water guide means whose configuration corresponds to the outer circumference of a roll, wherein the uniform distance relative to the roll produces an intermediate space between the cooling water guide means and the roll through which the cooling water is conveyed under pressure, which is supposed to achieve an average heat transfer number which is about four times the value of the conventional heat transfer number.
This known apparatus is technically very complicated and, in addition, the curvature adjusting members are arranged in such a way that they are not easily accessible and, moreover, the periodic readjustment of the curvature requires a high degree of maintenance work. Since, in addition, the cooling medium is conducted in a forced manner in a narrow gap along a portion of the roll surface, the cooling medium absorbs heat as it travels through the gap and looses its cooling intensity to the same extent.
The Japanese Patent Application published under the number 01091903 A discloses an apparatus for cooling the work rolls on the exit side with upper and lower cooling water guide plates provided with stripping members, wherein each cooling water guide plate is equipped at the end facing the work roll with spray nozzles for a cooling water and air mixture. By spraying a water mist into the corner areas between the work rolls and the rolling stock forming an acute angle on the exit side, a sufficient cooling effect is supposed to be achieved at the work rolls and the consumption of cooling water is simultaneously to be reduced.
The Japanese Patent Application published under number 01057908 A discloses water mist nozzles at the front side of cooling water guide plates, and additional upper and lower spray nozzles for cooling water. This apparatus is supposed to prevent the formation of cracks at the surface of the work rolls.
The Japanese Patent Application published under number 06339712 A discloses a cooling apparatus on the exit side for work rolls each with cooling water ducts arranged three-high above or below each other and equipped with spray nozzles, and with an upper and a lower cooling water guide plate with a stripping member at the end thereof. The upper guide plate is provided at a distance from the upper roll with a duct arranged parallel to the axis of the roll and provided with openings for cooling water to be discharged, wherein the duct forms a cooling water discharge duct which is open at both ends. This is supposed to achieve a discharge of heated cooling water from the middle portion of the work rolls uniformly to both sides. However, since the heated cooling water flows in this device only with natural gradient and through the relatively narrow duct cross-section from the middle toward both sides, the liquid throughput is relatively small and cannot be increased as desired.
The water level is adjusted between the upper cooling water guide plate and a lower portion of the upper work roll approximately on the level of the inlet openings of the discharge duct. In this construction the application of a negative pressure would only result in the intake of air, but not in an increased removal of liquid. Moreover, in this device it is also not possible to provide different discharge quantities of liquid in different areas of the discharge duct and in a direction extending parallel to the axis of the rolls which would mean that the formation of a predetermined thermal crown could be influenced. A discharge device for cooling water running off the lower work roll is not provided.